Pressure sensors can be used for control and monitoring of devices or to indirectly measure variables. For example, a pressure sensor usually acts as a transducer, generating an electrical signal as a function of the pressure imposed on the sensor.
Pressure sensors can vary drastically in technology, design, performance, application suitability and cost. For example, a capacitive pressure sensor uses a diaphragm, e.g., membrane or plate, to create a variable capacitor to detect strain due to applied pressure. In these systems, capacitance decreases as pressure deforms the diaphragm.
The capacitive pressure sensor can be fabricated using CMOS technologies. For example, using lithography, etching and deposition processes, a MEMS capacitor can be fabricated as a capacitive pressure sensor. In such a sensor, the top membrane of the MEMS capacitor is formed over a cavity structure, with the cavity structure above a bottom membrane (or plate). In this type of application, one or both of the membranes, for example, can be deflected into the cavity under an applied pressure, providing a change in capacitance between the two membranes. However, current fabrication processes cannot provide well-defined edges of the pressure sensor, leading to inaccurate readings and measurements.